This chapter’s guiding question is whether we should judge market exchanges unjust in light of their contribution to monopoly formation. The chapter first examines ways in which monopolies form quite generally – and shows that a series of seemingly just exchanges can give rise to a monopoly. The chapter then briefly outlines the typical effects of a monopolist using his market power. Namely, higher prices in comparison to competitive markets lead to inefficiencies and might spawn exploitative or coercive exchanges. But these most visible and widely discussed effects of monopolies do not constitute commutative injustice. This is because higher monopoly prices are a contingent consequence of monopoly formation, which depend on an intervening choice by the monopolist to use his market power exploitatively or coercively to maximize profits. The third part of the chapter then acknowledges that some monopolies are instances of domination – and that the market exchanges establishing them could be considered unjust in this light. However, this is not a consideration a liberal theory of justice in exchange needs to worry about.